Low luteal phase serum progesterone levels in regularly cycling women are predictive of subtle ovulation disorders.

Serial hormonal and ultrasound measurements were performed in a group of 50 infertile women with regular menstrual cycles of normal length, and evidence of luteinization by measurement of biphasic basal body temperature (BBT). The progesterone levels however, remained below a critical threshold of 32 nmol/l (1 nmol/l = 0.315 ng/ml) in two cycles. In 50 cycles, 25 showed definite abnormalities. In 16 other cycles, ovulation was observed, but relatively low luteal progesterone followed. Although pregnancy in these 16 cycles could be less likely, the real significance of this finding is questionable. The etiology of these 'subtle cycle anomalies' is not clear and may be multifactorial. For this reason, no therapy other than use of ovulation-inducing agents by trial and error is as yet available. Preliminary results indicate that cycle disturbances may persist under ovulation induction, even though progesterone levels are normalized.